The present invention is related to Japanese patent application No. 2000-127614, filed Apr. 24, 2000; the contents of which are incorporated herein by reference.
The present invention relates to a variable valve timing control apparatus of an internal combustion engine, and more particularly to a variable valve timing control apparatus for controlling open/close timing (referred to as valve timing below) of intake valves and/or exhaust valves corresponding to the operation condition of an internal combustion engine.
Internal combustion engines provided with a variable valve timing mechanism have become popular for improving engine output, saving fuel consumption, and reducing exhaust emission in vehicle internal combustion engines. In general, in a variable valve timing mechanism, engine oil pressure drives the valves. Oil pressure is controlled by an oil pressure control valve to variably control valve timing. Recently, to improve the response of such variable valve timing mechanisms, a variable valve timing control method providing consistent control regardless of the oil pressure is known. Here, oil pressure for driving a variable valve timing mechanism is estimated from oil temperature and engine speed, the target control magnitude of the oil pressure control valve is calculated based on the target advance angle that is set corresponding to the operation condition of the internal combustion engine, the correction gain corresponding to the target control magnitude is calculated corresponding to the oil pressure based on a map, the target control magnitude is corrected based on the correction gain, and the oil pressure control valve is controlled based on the corrected target control magnitude, as shown in Japanese Published Unexamined Patent Application No. Hei 7-91280.
However, the configuration described in the Japanese Published Unexamined Patent Application No. Hei 7-91280 requires a sensor for detecting the oil temperature (or oil pressure), and is resultantly disadvantageous because of the additional cost. Furthermore, though the correction gain is set corresponding to the oil pressure, it is difficult to satisfy both the response in a transitional state and the stability in a steady state. In other words, the stability in a steady state becomes poor if the correction gain is set larger to improve the response in a transitional state. On the other hand, the response in a transitional state becomes poor if the correction gain is set smaller to improve the stability in a steady state.
In light of these and other drawbacks, the present invention provides a variable valve timing control apparatus for an internal combustion engine that copes with both the response in a transitional state and stability in a steady state of variable valve timing control without additional cost. A variable valve timing control apparatus of an internal combustion engine sets a target advance angle of the valve timing corresponding to the operation condition of the internal combustion engine with a target advance angle setting means, determines the transitional or steady state operation condition with a transitional/steady state determining means when the valve timing is feedback-controlled to the target advance angle with a feedback control means, and variably sets the feedback gain of the feedback control based on the determination result obtained by a feedback gain variable means. Thereby, the feedback gain can be switched to the proper gain between transitional and steady states, and both the response in a transitional state and the stability in a steady state of the variable valve timing control are simultaneously satisfied. The throttle opening and intake air flow (or intake pipe pressure) detected by a sensor mounted on an engine control system are used to determine whether the operation condition is transitional or steady state. Therefore, an additional sensor is not required.
Furthermore, the target advance angle may be variably set based on the transitional or steady state determination result with a target advance angle variable means.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are intended for purposes of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.